|Publication number||US4956867 A|
|Application number||US 07/341,139|
|Publication date||Sep 11, 1990|
|Filing date||Apr 20, 1989|
|Priority date||Apr 20, 1989|
|Also published as||WO1990013215A1|
|Publication number||07341139, 341139, US 4956867 A, US 4956867A, US-A-4956867, US4956867 A, US4956867A|
|Inventors||Patrick M. Zurek, Julie E. Greenberg, Patrick M. Peterson|
|Original Assignee||Massachusetts Institute Of Technology|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (21), Non-Patent Citations (8), Referenced by (202), Classifications (9), Legal Events (9)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The United States Government has rights in this invention pursuant to Grant No. 5 R01 NS21322-04, sponsored by the National Institute of Health.
This invention relates to adaptive signal processing and, more particularly, to adaptive noise cancelling apparatus. The invention has application in systems where it is desired to reduce interference from noise sources that are spatially separate from a target source, e.g., in hearing aids, automatic speech recognition systems, telephony and microphone systems.
Adaptive signal processing systems are characterized by the capability to adjust their response in the face of changing, or time-variant, inputs. These systems are well suited to perform filtering tasks based on automatic "training" in which they continuously monitor their own previously-generated output signals to replace or remove specified components in presently-received input signals. While adaptive systems have broad applicability in areas such as prediction, modeling and equalization, of particular interest here is their application in interference cancelling, i.e., the removal of unwanted noise from input signals.
The prior art offers a variety of noise cancelling circuits. Among these are adaptive beamforming systems, which use spaced arrays of sensors, e.g., microphones, to reduce interference. A simple system, known as the Howells-Appelbaum sidelobe cancler, for example, employs two omnidirectional sensors for receiving input signals generated by target and interference sources. The system filters one of the input signals, the "reference," through an adaptive element and subtracts it from the other, the "primary." The output signal resulting from this subtraction is fed back to the adaptive element which adjusts the filter to minimize the difference between the filtered reference and primary signals. As the filter converges, the signal-to-noise ratio of the output improves--at least when interference dominates the input. See, for example, Widrow et al, Adaptive Signal Processing, Prentice Hall (1985), at pp. 302, et seq.
More complex beamforming systems proposed by Frost, and by Griffiths and Jim, among others, provide improved output signal-to-noise ratios under conditions where the input noise component is not dominant. See, Widrow et al, supra, and Griffiths, et al, "An Alternative Approach to Linearly Constrained Adaptive Beamforming," IEEE Transactions on Antennas and Propagation, vol. AP-30 (January 1982), at pp. 27, et seq.
Unfortunately, even these systems lose their effectiveness when the input becomes dominated by the target itself, or when a target-free sample of noise is not available. Here, the prior art adaptive systems degrade the target signal, producing an output with a lower signal-to-noise ratio than the input. This deficiency becomes of real concern where such beamforming circuits are incorporated into hearing aids and other applications where a target-free reference signal is unavailable and the system must operate at high, as well as low, signal-to-noise ratios.
In view of the foregoing, an object of this invention is to provide an improved adaptive beamforming system.
More particularly, an object of this invention is to provide an adaptive beamforming system which operates effectively over all ranges of input signal-to-noise ratios.
A further object of this invention is to provide an improved hearing aid which processes incoming signals using adaptive beamforming techniques and which continues to operate effectively even when there is relatively little interference in the input signals.
The aforementioned objects are attained by the invention, which provides, in one aspect, an adaptive noise cancelling apparatus which operates to overcome the problem encountered in conventional noise cancelling circuitry when the signal-to-noise ratio at the sensor array is high--to wit, that the target signal is degraded, leading to poorer intelligibility. In these instances, rather than allowing the adaptive filter to converge on filter values that degrade the target component of the output signal, a system constructed in accord with invention selectively inhibits adaptation, thereby preserving the target signal. To do this, the system takes advantage of momentary low signal-to-noise ratios, which are characteristic of human speech, for example, to converge to a desired filter response.
In another aspect, the invention provides an adaptive noise cancelling apparatus including an array of spatially disposed sensors, each arranged to receive an input signal having target and noise signal components, and an element coupled to the array for combining one or more of those input signals to form a primary signal. Another generator element is also coupled to the array to process the input signals to generate one or more reference signals representing only noise components of the input signals.
An adaptive filter produces a noise-approximating signal as a function of reference signals received over time and feeds that noise-approximating signal to an output element, which subtracts it from the primary to produce an output approximating the target signal.
A feedback path, including an adaptation controller, is coupled between the output elemebnt and the adaptive filter. The controller generates an adaptation signal as a function of the output signal and an SNR signal, which the controller generates from the input signals. More particularly, the controller is coupled with the sensor array for processing one or more of the input signals to generate the SNR signal as representative of the relative strength, over a short time, of the target signal to the noise signal. In one aspect, this SNR signal represents a cross-correlation between input signals received by two or more of the sensors.
The adaptative filter is coupled with the adaptation controller to receive the adaptation signal and to selectively modify the noise-approximating signal to minimize a difference between it and the primary signal. By providing that modified noise-approximating signal to the output element, the latter is able to generate an output signal more closely matching the target signal.
In one embodiment, the invention can provide an adaptive noise canceler of the type described above in which the adaptation controller includes a threshold detection element which generates a zero-valued adaptation signal if the SNR signal is in a first selected range, and for generating an adaptation signal which is equivalent to the output signal if the SNR signal is in a second selected range. In another embodiment, the adaptation controller can include a sliding scale element which generates an adaptation signal that varies with the SNR signal.
The adaptive noise cancelers of the present invention can further include filters within the adaptation controller for providing selected linear filterings of at least certain ones of the received input signals. According to another aspect of the invention, those filterings can be selected in accord with a range of expected delays in noise signal components received by selected ones of said sensor elements.
These and other aspects of the invention are evident in the drawings and in the detailed description which follows.
FIG. 1 depicts a two-microphone adaptive noise cancelling system constructed in accord with the invention.
FIG. 2 depicts a two-microphone adaptive noise cancelling system constructed in accord with a preferred embodiment of the invention indicating relationships between signals generated by system components.
FIG. 3 depicts preferred circuitry for sampling elements used to convert incoming sensor signals to digital form.
FIG. 4 depicts an M-microphone adaptive noise cancelling system constructed in accord with the invention.
FIG. 1 depicts a two-microphone adaptive noise cancelling system 10 constructed in accord with the invention. The illustrated system 10 includes a receiving array 12, sampling elements 13a, 13b, a primary signal generator 14, a reference signal generator 16, an adaptive filter 18, an output element 20, and an adaptation controller 22.
Receiving array 12 includes two sensors, e.g., microphones, 12a, 12b, spaced apart by a distance x and arranged to receive input signals having signal components from a target source 26 and noise sources 28a, 28b. In the illustrated embodiment, delays 24a, 24b are connected with the sensors 12a, 12b to steer the array 12, i.e., to delay input signals differentially to insure that target signal components received in the "look" direction y are in phase.
Sampling elements 13a, 13b sample the input-representative signals generated by array 12 and pass the sampled inputs on to other elements of the illustrated system. The sampling elements 13a, 13b are discussed in further detail below.
Primary signal generator 14 receives input signals from the sampling elements 13a, 13b over conductor lines 30a, 30b and generates a primary signal representative of a selected combination of those input signals. In a preferred embodiment, generator 14 comprises a summation element 32 for adding the input signals, as well as a filter element 34, which may include a delay to simulate non-causal impulse responses of the adaptive filter. The primary signal is transmitted from the generator 14 to the output element over conductor line 35.
The reference signal generator 16 also receives input signals from the samplers 13a, 13b over conductor lines 30a, 30b to produce a reference signal representing components of the noise signal. The illustrated generator 16 produces that reference signal by subtracting input signals received by one sensor 12b from those received by the other 12a. Output from the reference signal generator 16 is transmitted to the adaptive filter 18 over conductor line 36, as indicated in the drawing.
The adaptive filter 18 generates a signal which approxmates the value of the noise signal. This approximation is based on the noise component signals received from the reference signal generator 16 over a selected period of time. For this purpose, the illustrated filter 18 includes a tapped delay line 38 having a plurality of "taps," or stores, which retain values of reference signals generated during the past L timing intervals, where L is referred to as the length of the adaptive filter. The tapped delay line 38 also includes a set of weighting elements 40a, 40b, . . . , 40c which store mathematical weights associated with each of the L taps. A linear combiner 42 is coupled to the taps and to the weighting elements for generating the noise-approximating signal as a sum of the multiplicative products of each of the stored reference signals and the associated weights. That noise-approximating signal is transmitted to the output element 20 over line 46.
Output element 20 generates an output signal, representing the signal generated by the target 26, by subtracting the primary signal, received over conductor line 35, from the noise-approximating signal, received over line 46. In a preferred hearing-aid embodiment, that output signal can be passed over line 47 to a digital-to-analog converter, a low-pass filter 48, an amplifier 50, and a speaker 52 to provide an audible signal suitable for the hearing-aid user. The output signal is also routed over line 47 to the adaptation controller 22.
The adaptation controller 22 processes input signals received over lines 30a, 30b to generate an SNR signal representing a relative strength of the target signal to the noise signal. In the illustrated system, the SNR signal is produced by first passing each of the sampled input signals through fixed linear filters 54a, 54b, selected according to the range of expected delays in the noise signal components received by the sensors 12a, 12b.
The outputs of filters 54a, 54b are then passed to an element 56 which, in accord with a preferred embodiment, generates the SNR signal from a running cross-correlation of the filtered input signals. Through the element 56 can produce the SNR signal by multiplying the values represented by the filtered input signals, preferably, it simply estimates the cross-correlation by multiplying the polarity of those inputs.
In the illustrated embodiment, the SNR sgnal is passed to a threshold detection element 58 which generates an adaptation signal having a value of zero if the SNR signal is in a first selected range and having a value equal to that of the output signal (received over line 47) if the SNR signal is in a second selected range. Where the SNR signal represents an estimate of the input signal cross-correlation--as opposed to another estimate of target signal strength to noise signal strength--a zero-valued adaptation signal is generated in response to a cross-correlation signal having a value above a preselected threshold, and an output signal-equivalent adaptation signal otherwise.
In another preferred embodiment, the adaptation element 22 can include a sliding scale element which generates an adaptation signal having a value which varies, e.g., monotonically, with the SNR signal.
The adaptation signal generated by the adaptation controller 22 is transmitted to modification element 44 over conductor line 60. Element 44 adjusts the weight-representative signals in response to that adaptation signal to minimize a difference between the noise-approximating signal and the primary signal.
A fuller appreciation of the operation of the adaptive noise canceler 10 may be understood as follows. The sensor array 12 receives input signals generated by the target source 26 and the noise source 28. As a result of the positioning of the sensors, and/or the delays effected by the steering elements 24a, 24b, the array 12 produces input-representative signals having target signal components which are nearly in phase and noise signal components which are substantially out of phase.
Generator 14 combines the input signals to produce a primary signal, having both target and noise components, which is a sum of the input signals. Simultaneously, generator 16 subtracts the input signals from one another to produce a reference signal having predominantly noise components. The reference signal is fed into the adaptive filter 18 which produces a noise-approximating signal based on a weighted sum of current and past values of the reference signal.
Subtracting this noise-approximating signal from the primary signal, output element 20 produces an output signal approximating the target signal.
To improve the quality of the output signal, the adaptive filter 18 continuously monitors the adaptation signal, generated by controller 22, to determine if the weighting values require adjustment. In this regard, it will be appreciated that the power of the output signal falls to a minimum when that signal contains only target signal components.
To prevent degradation of the target signal when it dominates the beamformer input, the illustrated adaptation controller 22 reduces the adaptation signal to zero when it determines that the cross-correlation of the input signal is high. The filter 18 interprets that zero-valued signal as an indication that the input target-to-noise ratio is high and, accordingly, freezes the current weight values. Where, on the other hand, the cross-correlation is low, the controller 22 generates an adaptation signal equal in value to the output signal, so that the filter 18 can further adjust the weights, if necessary, to minimize the power output.
In this light, it is clear that the filters 54a, 54b function to pass those frequencies of the input signals which are most likely to indicate the presence of noise, i.e., those which will experience the greatest decorrelation given the particular spacing of the sensors 12a, 12b.
A further understanding of the operation of a preferred embodiment of the beamforming system 10 may be attained by reference to FIG. 2 and to the chart below, which together present in mathematical from the values of signals generated by the system components. The circuit of FIG. 2 is similar to that of FIG. 1 and, accordingly, uses like element designations.
In FIG. 2, the value of signals transmitted between components are denoted adjacent the conductor lines connecting those components. A more complete expression of those values is given in Table 1, below. Thus, for example, input signals passed from the sensor array 12 to the primary signal generator 14 and the reference signal generator 16 are denoted m1 [n] and m2 [n]. Upon processing by summation element 32 of the primary signal generator 14, the input signals are combined to form the primary signal, s[n], which Table 1 indicates as having a value equal to one-half the sum of the sensor signals, i.e., (m1 [n][m2 [n])/2. The remaining signal values shown in the drawing can be interpreted in a like manner.
TABLE 1______________________________________Signal Value/Description______________________________________d[n] 1/2 × (m1 [n] - m2 [n])fj [n] the sum of (mj [n - i] × gi), for i = to N - 1, and for j = 1, 2m1 [n] input-representative signal from sensor 12am2 [n] input-representative signal from sensor 12br[n] 0.99 × r[n - 1] + 0.01 × f[n], where f[n] = +1, if f1 [n] × f2 [n] > 0, and f[n] = -1, if f1 [n] × f2 [n] < 0v[n] the sum of (d[n - k] × wk [n]), for k = 0 to (L - 1)s[n] 1/2 × (m1 [n] + m2 [ n])t[n] 0, if r[n] > threshold constant, and y[n], if r[n] < threshold constanty[n] s[n - (L - 1)/2] - v[n], for odd values of L______________________________________
In Table 1 and FIG. 2, bracket notation is used to denote the value of each signal at specific time intervals. Thus m1 [n], m2 [n] and y[n] represent input and beamformer output sgnal values, respectively, at timing interval n, where n is an integer. It will be noted that the signal output by element 34 also includes a time component; however, unlike that of the other system elements, the element 34 output is delayed (L-1)/2 timing intervals, a time period equal to roughly half the length of the adaptive filter 16. Those skilled in the art will appreciate that such a delay simulates a non-causal impulse response; that is, it permits the adaptive filter 18 to employ values of the reference signal d[n] received both before and after the primary signal.
Consistent with the above notation, the modification element 44 (FIG. 1) adjusts the weights used in the adaptive filter 18 in accord with an unconstrained least squares algorithm and based upon a power value q[n] equal to 0.9941×p[n-1]+0.0059×p[n], where p[n] is equal to (y[n])2 +(d[n])2 ; a weight-delta value D[n] equal to 2×A×(t[n])/(L×(q[n])); and weight update values Wk [n+1] equal to Wk [n]+(D[n])×(d[n-k]), where Wk represents a weight associated with a kth tap in delay line 38 and where k is an integer between 0 and (L-1).
A preferred beamforming system 10 intended for use in a hearing aid, assuming a sampling frequency of 10 kHz, has an adaptive filter length, L, between 5 and 500 samples, with a preferred value of 169; a correlation filter length, N, between 5 and 500, with a preferred value of 100; an adaptation constant, A, between 0.005 and 0.5, with a preferred value of 0.05; and a threshold constant between -0.5 and +0.5, with a preferred value of 0.0.
In a preferred embodiment, the beamforming system 10 is implemented using two Motorola DSP56000ADS signal processing boards: one for performing the functions of the primary signal generator 14, the reference signal generator 16, the adaptive filter 18 and the output element 20; and the other, for performing the functions of the adaptation element 22.
The aforementioned system 10 employs a digital-to-analog converter 51 interposed between the output element 20 and low-pass filter 48. The system also employs sampling elements 13a, 13b of the type depicted in FIG. 3 for converting incoming target and noise signals to digital form.
Referring to FIG. 3, samplers 13a, 13b include, respectively, amplifiers 64a, 64b, low-pass filters 66a, 66b and analog-to-digital converters 68a, 68b. Each samplers 13a, 13b is coupled to a microphone 12a, 12b (FIG. 1) and preamplifier (not shown) of the array 12 (FIG. 1). Amplified input-representative signals, generated by amplifiers 64a, 64;I b, are filtered through low-pass filters 66a, 66b, selected to pass target and noise signal frequencies less than one-half the sampling frequency.
Filtered input signals from both illustrated channels are sampled by analog-to-digital converters 68a, 68b, which are driven by external clock 70. The digital outputs of the converters 68a, 68b are passed, via lines 30a, 30b, respectively, to the primary signal-generator 14, reference signal-generator 16, and adaptation controller 22 for processing in the manner described above.
In a preferred embodiment intended for use in conjunction with a hearing aid, the low-pass filters 66a, 66b are selected to pass frequencies below 4.5 kHz, and the sampling rate of the A/D converters 68a, 68b is set at 10 kHz.
The above teachings can be applied, more generally, to an (M-1) sensor beamforming system constructed and operated in accord with the invention, where M is an integer greater than or equal to two. One such system is depicted in FIG. 4. The illustrated system 80 includes a receiving array 82, a primary signal generator 84, (M-1) beamforming sections 861, 862, . . . 86M-1, and output element 88. Each beamforming section includes a reference signal generator 921, 922, . . . 92M-1, an adaptive filter (which can include a modification element, now shown) 941, 942, . . . 94M-1, and a adaptation controller 961, 962, . . . 96M-1. These elements are constructed and operated in accord with the teachings of similarly-named elements shown in FIGS. 1 and 2, described above.
Particularly, receiving array 82 includes a plurality of sensors 821, 822, . . . 82M-1, 82M, each having a corresponding steering delay 901, 902, 903, . . . 90M-1, 90M. As illustrated, the outputs of the array 82 are passed to the primary signal generator 84. Likewise, the outputs of pairs of those sensors are passed to the reference signal generators 921, 922, . . . 92M-1 and to the adaptation controllers 961, 962, . . . 96M-1.
As above, the reference signal generators and adaptation controllers pass their output--representative, respectively, of reference and adaptation signals corresponding to associated pairs of the sensors--to corresponding adaptive filters (and modification element) 941, 942, . . . 94M-1. These adaptive filters produce noise-component approximating signals which approximate the noise signal components received from the associated sensor pairs based on a time-wise sample of those components. The output of the filters 941, 942, . . . 94M-1 are routed to the output element 88, which subtracts them from the primary signal, thereby producing an output signal matching the target signal.
The foregoing describes improved adaptive beamforming systems which can be constructed using a plurality of sensors to reduce interference from noise sources that are spatially separate from a target source. These improved systems operate effectively over all ranges of input signal-to-noise ratios and, unlike prior art systems, do not suffer target signal degradation when input signal-to-noise ratios are high.
Those skilled in the art will appreciate that the illustrated embodiments described above are exemplary only, and that modifications, additions and deletions can made thereto without falling outside the scope or spirit of this invention: for example, that at least portions of the systems described above can be constructed to process analog, as well as digital, signals; that the SNR signals can be generated as a function of the input received from one, as well as many, sensors; that the adaptation controller can employ a combination of threshold and sliding scale elements; and that the adaptive filter can employ any of a number of known weight-modification algorithms, in addition to the unconstrained least squares algorithm.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3057960 *||Mar 13, 1961||Oct 9, 1962||Bell Telephone Labor Inc||Normalized sound control system|
|US3109066 *||Dec 15, 1959||Oct 29, 1963||Bell Telephone Labor Inc||Sound control system|
|US3882498 *||Feb 22, 1973||May 6, 1975||Gen Electric||Adaptive array processor providing improved mainlobe maintenance|
|US4079380 *||Nov 22, 1976||Mar 14, 1978||Motorola, Inc.||Null steering apparatus for a multiple antenna array on an FM receiver|
|US4214244 *||Dec 20, 1971||Jul 22, 1980||Martin Marietta Corporation||Null pattern technique for reduction of an undesirable interfering signal|
|US4286268 *||Apr 13, 1979||Aug 25, 1981||Motorola Inc.||Adaptive array with optimal sequential gradient control|
|US4548082 *||Aug 28, 1984||Oct 22, 1985||Central Institute For The Deaf||Hearing aids, signal supplying apparatus, systems for compensating hearing deficiencies, and methods|
|US4641259 *||Jan 23, 1984||Feb 3, 1987||The Board Of Trustees Of The Leland Stanford Junior University||Adaptive signal processing array with suppession of coherent and non-coherent interferring signals|
|US4651155 *||May 28, 1982||Mar 17, 1987||Hazeltine Corporation||Beamforming/null-steering adaptive array|
|US4686532 *||May 31, 1985||Aug 11, 1987||Texas Instruments Incorporated||Accurate location sonar and radar|
|US4688187 *||Jul 3, 1984||Aug 18, 1987||Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland||Constraint application processor for applying a constraint to a set of signals|
|US4713668 *||Sep 18, 1986||Dec 15, 1987||Stc Plc||Adaptive antenna|
|US4723294 *||Dec 8, 1986||Feb 2, 1988||Nec Corporation||Noise canceling system|
|US4752969 *||Jan 16, 1986||Jun 21, 1988||Kenneth Rilling||Anti-multipath signal processor|
|US4754282 *||Mar 25, 1970||Jun 28, 1988||The United States Of America As Represented By The Secretary Of The Navy||Improved data analysis system|
|US4758999 *||Dec 3, 1985||Jul 19, 1988||The Commonwealth Of Australia||Systolic architectures for sonar processing|
|US4769847 *||Oct 30, 1986||Sep 6, 1988||Nec Corporation||Noise canceling apparatus|
|US4771289 *||Feb 20, 1987||Sep 13, 1988||Hazeltine Corporation||Beamforming/null-steering adaptive array|
|US4806939 *||Dec 31, 1985||Feb 21, 1989||Stc, Plc||Optimization of convergence of sequential decorrelator|
|US4811404 *||Oct 1, 1987||Mar 7, 1989||Motorola, Inc.||Noise suppression system|
|WO1986001057A1 *||Jul 18, 1985||Feb 13, 1986||The Commonwealth Of Australia Care Of The Secretar||Adaptive antenna array|
|1||"An Alternative Approach to Linearly . . . ", Griffiths et al., IEEE Transactions on Antennas . . . , vol. AP-30, No. 1, 1/82, pp. 27-34.|
|2||"Multimicrophone Adaptive Beamforming . . . ", Peterson et al., Submitted to the Journal of Rehabilitation Rsrch and Devel., 11/86.|
|3||"Multimicrophone Monaural Hearing Aids," Durlach et al., RESNA 10th Annual Conference, San Jose, CA, 1987.|
|4||"Using Linearly-Constrained Adaptive . . . ", P. M. Peterson, Proceedings of ICASSP, Int'l Conf on . . . , 4/6-9/87, pp. 2364-2367.|
|5||*||An Alternative Approach to Linearly . . . , Griffiths et al., IEEE Transactions on Antennas . . . , vol. AP 30, No. 1, 1/82, pp. 27 34.|
|6||*||Multimicrophone Adaptive Beamforming . . . , Peterson et al., Submitted to the Journal of Rehabilitation Rsrch and Devel., 11/86.|
|7||*||Multimicrophone Monaural Hearing Aids, Durlach et al., RESNA 10 th Annual Conference, San Jose, CA, 1987.|
|8||*||Using Linearly Constrained Adaptive . . . , P. M. Peterson, Proceedings of ICASSP, Int l Conf on . . . , 4/6 9/87, pp. 2364 2367.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5233665 *||Dec 17, 1991||Aug 3, 1993||Gary L. Vaughn||Phonetic equalizer system|
|US5237618 *||May 11, 1990||Aug 17, 1993||General Electric Company||Electronic compensation system for elimination or reduction of inter-channel interference in noise cancellation systems|
|US5347586 *||Apr 28, 1992||Sep 13, 1994||Westinghouse Electric Corporation||Adaptive system for controlling noise generated by or emanating from a primary noise source|
|US5416846 *||May 25, 1994||May 16, 1995||Matsushita Electric Industrial Co., Ltd.||Noise control system and method|
|US5473701 *||Nov 5, 1993||Dec 5, 1995||At&T Corp.||Adaptive microphone array|
|US5482036 *||May 26, 1994||Jan 9, 1996||Masimo Corporation||Signal processing apparatus and method|
|US5490505 *||Oct 6, 1993||Feb 13, 1996||Masimo Corporation||Signal processing apparatus|
|US5500902 *||Jul 8, 1994||Mar 19, 1996||Stockham, Jr.; Thomas G.||Hearing aid device incorporating signal processing techniques|
|US5533063 *||Jan 31, 1994||Jul 2, 1996||The Regents Of The University Of California||Method and apparatus for multipath channel shaping|
|US5574824 *||Apr 14, 1995||Nov 12, 1996||The United States Of America As Represented By The Secretary Of The Air Force||Analysis/synthesis-based microphone array speech enhancer with variable signal distortion|
|US5581495 *||Sep 23, 1994||Dec 3, 1996||United States Of America||Adaptive signal processing array with unconstrained pole-zero rejection of coherent and non-coherent interfering signals|
|US5627799 *||Sep 1, 1995||May 6, 1997||Nec Corporation||Beamformer using coefficient restrained adaptive filters for detecting interference signals|
|US5632272 *||Oct 7, 1994||May 27, 1997||Masimo Corporation||Signal processing apparatus|
|US5662105 *||May 17, 1995||Sep 2, 1997||Spacelabs Medical, Inc.||System and method for the extractment of physiological signals|
|US5685299 *||Dec 14, 1995||Nov 11, 1997||Masimo Corporation||Signal processing apparatus|
|US5687722 *||Jul 26, 1995||Nov 18, 1997||Spacelabs Medical, Inc.||System and method for the algebraic derivation of physiological signals|
|US5769785 *||Jun 7, 1995||Jun 23, 1998||Masimo Corporation||Signal processing apparatus and method|
|US5797852 *||Jun 7, 1995||Aug 25, 1998||Local Silence, Inc.||Sleep apnea screening and/or detecting apparatus and method|
|US5825898 *||Jun 27, 1996||Oct 20, 1998||Lamar Signal Processing Ltd.||System and method for adaptive interference cancelling|
|US5848163 *||Feb 2, 1996||Dec 8, 1998||International Business Machines Corporation||Method and apparatus for suppressing background music or noise from the speech input of a speech recognizer|
|US5848171 *||Jan 12, 1996||Dec 8, 1998||Sonix Technologies, Inc.||Hearing aid device incorporating signal processing techniques|
|US5917921 *||Apr 17, 1995||Jun 29, 1999||Sony Corporation||Noise reducing microphone apparatus|
|US5937070 *||Oct 2, 1995||Aug 10, 1999||Todter; Chris||Noise cancelling systems|
|US6002952 *||Apr 14, 1997||Dec 14, 1999||Masimo Corporation||Signal processing apparatus and method|
|US6036642 *||Jun 22, 1998||Mar 14, 2000||Masimo Corporation||Signal processing apparatus and method|
|US6067462 *||May 19, 1998||May 23, 2000||Masimo Corporation||Signal processing apparatus and method|
|US6081735 *||Jul 3, 1997||Jun 27, 2000||Masimo Corporation||Signal processing apparatus|
|US6157850 *||May 16, 1997||Dec 5, 2000||Masimo Corporation||Signal processing apparatus|
|US6171258||Oct 8, 1998||Jan 9, 2001||Sleep Solutions, Inc.||Multi-channel self-contained apparatus and method for diagnosis of sleep disorders|
|US6178248||Apr 14, 1997||Jan 23, 2001||Andrea Electronics Corporation||Dual-processing interference cancelling system and method|
|US6206830||Nov 17, 1999||Mar 27, 2001||Masimo Corporation||Signal processing apparatus and method|
|US6213955||Oct 8, 1998||Apr 10, 2001||Sleep Solutions, Inc.||Apparatus and method for breath monitoring|
|US6236872||Nov 25, 1998||May 22, 2001||Masimo Corporation||Signal processing apparatus|
|US6263222||Oct 6, 1997||Jul 17, 2001||Masimo Corporation||Signal processing apparatus|
|US6290654||Oct 8, 1998||Sep 18, 2001||Sleep Solutions, Inc.||Obstructive sleep apnea detection apparatus and method using pattern recognition|
|US6363345||Feb 18, 1999||Mar 26, 2002||Andrea Electronics Corporation||System, method and apparatus for cancelling noise|
|US6408318||Apr 5, 1999||Jun 18, 2002||Xiaoling Fang||Multiple stage decimation filter|
|US6480610||Sep 21, 1999||Nov 12, 2002||Sonic Innovations, Inc.||Subband acoustic feedback cancellation in hearing aids|
|US6501975||Jan 9, 2001||Dec 31, 2002||Masimo Corporation||Signal processing apparatus and method|
|US6529605||Jun 29, 2000||Mar 4, 2003||Harman International Industries, Incorporated||Method and apparatus for dynamic sound optimization|
|US6563931||Jul 29, 1992||May 13, 2003||K/S Himpp||Auditory prosthesis for adaptively filtering selected auditory component by user activation and method for doing same|
|US6594367||Oct 25, 1999||Jul 15, 2003||Andrea Electronics Corporation||Super directional beamforming design and implementation|
|US6603858 *||Jun 1, 1998||Aug 5, 2003||The University Of Melbourne||Multi-strategy array processor|
|US6650917||Dec 4, 2001||Nov 18, 2003||Masimo Corporation||Signal processing apparatus|
|US6699194||Apr 11, 2000||Mar 2, 2004||Masimo Corporation||Signal processing apparatus and method|
|US6738481||Jan 10, 2001||May 18, 2004||Ericsson Inc.||Noise reduction apparatus and method|
|US6741713 *||Dec 17, 1998||May 25, 2004||Sonionmicrotronic Nederlan B.V.||Directional hearing device|
|US6745060||Dec 3, 2001||Jun 1, 2004||Masimo Corporation||Signal processing apparatus|
|US6751325 *||Sep 17, 1999||Jun 15, 2004||Siemens Audiologische Technik Gmbh||Hearing aid and method for processing microphone signals in a hearing aid|
|US6757395||Jan 12, 2000||Jun 29, 2004||Sonic Innovations, Inc.||Noise reduction apparatus and method|
|US6801632||Oct 10, 2001||Oct 5, 2004||Knowles Electronics, Llc||Microphone assembly for vehicular installation|
|US6822928 *||Apr 14, 2003||Nov 23, 2004||The United States Of America As Represented By The Secretary Of The Navy||Adaptive sonar signal processing method and system|
|US6823086 *||Aug 29, 2000||Nov 23, 2004||Analogic Corporation||Adaptive spatial filter|
|US6826419||Dec 20, 2002||Nov 30, 2004||Masimo Corporation||Signal processing apparatus and method|
|US6836679||Feb 5, 2002||Dec 28, 2004||Nellcor Puritan Bennett Incorporated||Method and apparatus for estimating physiological parameters using model-based adaptive filtering|
|US6931123 *||Apr 7, 1999||Aug 16, 2005||British Telecommunications Public Limited Company||Echo cancellation|
|US6980611 *||Feb 3, 2000||Dec 27, 2005||Scientific Applications & Research Associates, Inc.||System and method for measuring RF radiated emissions in the presence of strong ambient signals|
|US6999541||Nov 12, 1999||Feb 14, 2006||Bitwave Pte Ltd.||Signal processing apparatus and method|
|US7013015 *||Mar 1, 2002||Mar 14, 2006||Siemens Audiologische Technik Gmbh||Method for the operation of a hearing aid device or hearing device system as well as hearing aid device or hearing device system|
|US7020297||Dec 15, 2003||Mar 28, 2006||Sonic Innovations, Inc.||Subband acoustic feedback cancellation in hearing aids|
|US7079606 *||Oct 9, 2001||Jul 18, 2006||Mitsubishi Denki Kabushiki Kaisha||Method of obtaining an antenna gain|
|US7130671||Feb 9, 2004||Oct 31, 2006||Nellcor Puritan Bennett Incorporated||Pulse oximeter sensor off detector|
|US7155019||Mar 14, 2001||Dec 26, 2006||Apherma Corporation||Adaptive microphone matching in multi-microphone directional system|
|US7194293||Mar 8, 2004||Mar 20, 2007||Nellcor Puritan Bennett Incorporated||Selection of ensemble averaging weights for a pulse oximeter based on signal quality metrics|
|US7206421||Jul 14, 2000||Apr 17, 2007||Gn Resound North America Corporation||Hearing system beamformer|
|US7215984||May 4, 2004||May 8, 2007||Masimo Corporation||Signal processing apparatus|
|US7215986||Jun 15, 2005||May 8, 2007||Masimo Corporation||Signal processing apparatus|
|US7242781||May 15, 2001||Jul 10, 2007||Apherma, Llc||Null adaptation in multi-microphone directional system|
|US7254433||Sep 30, 2003||Aug 7, 2007||Masimo Corporation||Signal processing apparatus|
|US7280627||Dec 8, 2003||Oct 9, 2007||The Johns Hopkins University||Constrained data-adaptive signal rejector|
|US7289586||Dec 5, 2005||Oct 30, 2007||Bitwave Pte Ltd.||Signal processing apparatus and method|
|US7302062||Mar 21, 2005||Nov 27, 2007||Harman Becker Automotive Systems Gmbh||Audio enhancement system|
|US7302284||Jan 19, 2005||Nov 27, 2007||Nellcor Puritan Bennett Llc||Pulse oximeter with parallel saturation calculation modules|
|US7315753||Mar 22, 2004||Jan 1, 2008||Nellcor Puritan Bennett Llc||Pulse oximeter with parallel saturation calculation modules|
|US7328053||Nov 17, 1998||Feb 5, 2008||Masimo Corporation||Signal processing apparatus|
|US7336983||Apr 18, 2006||Feb 26, 2008||Nellcor Puritan Bennett Llc||Pulse oximeter with parallel saturation calculation modules|
|US7346175||Jul 2, 2002||Mar 18, 2008||Bitwave Private Limited||System and apparatus for speech communication and speech recognition|
|US7376453||Sep 1, 1998||May 20, 2008||Masimo Corporation||Signal processing apparatus|
|US7383070||Dec 3, 2004||Jun 3, 2008||Masimo Corporation||Signal processing apparatus|
|US7415372||Aug 26, 2005||Aug 19, 2008||Step Communications Corporation||Method and apparatus for improving noise discrimination in multiple sensor pairs|
|US7436188||Aug 26, 2005||Oct 14, 2008||Step Communications Corporation||System and method for improving time domain processed sensor signals|
|US7454240||May 11, 2006||Nov 18, 2008||Masimo Corporation||Signal processing apparatus|
|US7471799 *||Jun 21, 2002||Dec 30, 2008||Oticon A/S||Method for noise reduction and microphonearray for performing noise reduction|
|US7471971||Mar 2, 2004||Dec 30, 2008||Masimo Corporation||Signal processing apparatus and method|
|US7472041||Aug 26, 2005||Dec 30, 2008||Step Communications Corporation||Method and apparatus for accommodating device and/or signal mismatch in a sensor array|
|US7474907||Feb 1, 2007||Jan 6, 2009||Nellcor Puritan Bennett Inc.||Selection of ensemble averaging weights for a pulse oximeter based on signal quality metrics|
|US7489958||May 3, 2006||Feb 10, 2009||Masimo Corporation||Signal processing apparatus and method|
|US7496393||Sep 30, 2003||Feb 24, 2009||Masimo Corporation||Signal processing apparatus|
|US7499741||May 4, 2004||Mar 3, 2009||Masimo Corporation||Signal processing apparatus and method|
|US7509154||Aug 20, 2007||Mar 24, 2009||Masimo Corporation||Signal processing apparatus|
|US7530955||May 4, 2004||May 12, 2009||Masimo Corporation||Signal processing apparatus|
|US7619563||Nov 17, 2009||Step Communications Corporation||Beam former using phase difference enhancement|
|US7788066||Aug 31, 2010||Dolby Laboratories Licensing Corporation||Method and apparatus for improving noise discrimination in multiple sensor pairs|
|US7865224||Oct 12, 2004||Jan 4, 2011||Nellcor Puritan Bennett Llc||Method and apparatus for estimating a physiological parameter|
|US7890154||Dec 3, 2008||Feb 15, 2011||Nellcor Puritan Bennett Llc||Selection of ensemble averaging weights for a pulse oximeter based on signal quality metrics|
|US7931599||Apr 26, 2011||Nellcor Puritan Bennett Llc||Method and apparatus for estimating a physiological parameter|
|US7937130||Dec 19, 2008||May 3, 2011||Masimo Corporation||Signal processing apparatus|
|US7962190||Jun 14, 2011||Masimo Corporation||Signal processing apparatus|
|US8019400||Aug 20, 2007||Sep 13, 2011||Masimo Corporation||Signal processing apparatus|
|US8036728||Oct 11, 2011||Masimo Corporation||Signal processing apparatus|
|US8046041||Jun 21, 2007||Oct 25, 2011||Masimo Corporation||Signal processing apparatus|
|US8046042||Oct 25, 2011||Masimo Corporation||Signal processing apparatus|
|US8085943 *||Nov 29, 2000||Dec 27, 2011||Bizjak Karl M||Noise extractor system and method|
|US8085959||Sep 8, 2004||Dec 27, 2011||Brigham Young University||Hearing compensation system incorporating signal processing techniques|
|US8111192||Oct 30, 2009||Feb 7, 2012||Dolby Laboratories Licensing Corporation||Beam former using phase difference enhancement|
|US8116481||Apr 25, 2006||Feb 14, 2012||Harman Becker Automotive Systems Gmbh||Audio enhancement system|
|US8126528||Mar 24, 2009||Feb 28, 2012||Masimo Corporation||Signal processing apparatus|
|US8128572||Nov 24, 2008||Mar 6, 2012||Masimo Corporation||Signal processing apparatus|
|US8139787||Sep 8, 2006||Mar 20, 2012||Simon Haykin||Method and device for binaural signal enhancement|
|US8147544||Oct 26, 2002||Apr 3, 2012||Otokinetics Inc.||Therapeutic appliance for cochlea|
|US8155926||Dec 29, 2008||Apr 10, 2012||Dolby Laboratories Licensing Corporation||Method and apparatus for accommodating device and/or signal mismatch in a sensor array|
|US8155927||Aug 2, 2010||Apr 10, 2012||Dolby Laboratories Licensing Corporation||Method and apparatus for improving noise discrimination in multiple sensor pairs|
|US8170221||May 1, 2012||Harman Becker Automotive Systems Gmbh||Audio enhancement system and method|
|US8180420||Aug 20, 2007||May 15, 2012||Masimo Corporation||Signal processing apparatus and method|
|US8190227||Feb 9, 2009||May 29, 2012||Masimo Corporation||Signal processing apparatus and method|
|US8249271||Aug 21, 2012||Karl M. Bizjak||Noise analysis and extraction systems and methods|
|US8359080||Jan 22, 2013||Masimo Corporation||Signal processing apparatus|
|US8364226||Feb 9, 2012||Jan 29, 2013||Masimo Corporation||Signal processing apparatus|
|US8379875||Feb 19, 2013||Nokia Corporation||Method for efficient beamforming using a complementary noise separation filter|
|US8428275 *||Jun 19, 2008||Apr 23, 2013||Sanyo Electric Co., Ltd.||Wind noise reduction device|
|US8463349||May 3, 2012||Jun 11, 2013||Masimo Corporation||Signal processing apparatus|
|US8560034||Jul 6, 1998||Oct 15, 2013||Masimo Corporation||Signal processing apparatus|
|US8560036||Dec 28, 2010||Oct 15, 2013||Covidien Lp||Selection of ensemble averaging weights for a pulse oximeter based on signal quality metrics|
|US8571855||Jul 20, 2005||Oct 29, 2013||Harman Becker Automotive Systems Gmbh||Audio enhancement system|
|US8611548||Jul 23, 2012||Dec 17, 2013||Karl M. Bizjak||Noise analysis and extraction systems and methods|
|US8755856||Feb 22, 2012||Jun 17, 2014||Masimo Corporation||Signal processing apparatus|
|US8767973 *||Nov 8, 2011||Jul 1, 2014||Andrea Electronics Corp.||Adaptive filter in a sensor array system|
|US8876689||Apr 2, 2012||Nov 4, 2014||Otokinetics Inc.||Hearing aid microactuator|
|US8888708||May 14, 2012||Nov 18, 2014||Masimo Corporation||Signal processing apparatus and method|
|US8942777||May 25, 2007||Jan 27, 2015||Masimo Corporation||Signal processing apparatus|
|US8948834||Mar 2, 2005||Feb 3, 2015||Masimo Corporation||Signal processing apparatus|
|US9014386||Feb 13, 2012||Apr 21, 2015||Harman Becker Automotive Systems Gmbh||Audio enhancement system|
|US9078057 *||Nov 1, 2012||Jul 7, 2015||Csr Technology Inc.||Adaptive microphone beamforming|
|US9289167||Dec 5, 2012||Mar 22, 2016||Masimo Corporation||Signal processing apparatus and method|
|US9392360||Jun 30, 2014||Jul 12, 2016||Andrea Electronics Corporation||Steerable sensor array system with video input|
|US9425757 *||May 15, 2013||Aug 23, 2016||Infineon Technologies Ag||Apparatus and method for controlling an amplification gain of an amplifier, and a digitizer circuit and microphone assembly|
|US20020013906 *||Jun 14, 2001||Jan 31, 2002||Walter Wallach||Secure medical test and result delivery system|
|US20020031234 *||Jun 27, 2001||Mar 14, 2002||Wenger Matthew P.||Microphone system for in-car audio pickup|
|US20020034310 *||Mar 14, 2001||Mar 21, 2002||Audia Technology, Inc.||Adaptive microphone matching in multi-microphone directional system|
|US20020105465 *||Oct 9, 2001||Aug 8, 2002||Mitsubishi Denki Kabushiki Kaisha||Method of obtaining an antenna gain|
|US20020138254 *||Mar 20, 2002||Sep 26, 2002||Takehiko Isaka||Method and apparatus for processing speech signals|
|US20020172374 *||Nov 29, 2000||Nov 21, 2002||Bizjak Karl M.||Noise extractor system and method|
|US20020176594 *||Mar 1, 2002||Nov 28, 2002||Volker Hohmann||Method for the operation of a hearing aid device or hearing device system as well as hearing aid device or hearing device system|
|US20030050994 *||Jul 27, 2001||Mar 13, 2003||Robert Pollack||Method of aggregating, classifying, reporting and cross-tabbing data in real time|
|US20030177007 *||Mar 14, 2003||Sep 18, 2003||Kabushiki Kaisha Toshiba||Noise suppression apparatus and method for speech recognition, and speech recognition apparatus and method|
|US20040064020 *||Sep 30, 2003||Apr 1, 2004||Diab Mohamed K.||Signal processing apparatus|
|US20040120429 *||Dec 8, 2003||Jun 24, 2004||Orlin David J.||Constrained data-adaptive signal rejector|
|US20040125962 *||Apr 13, 2001||Jul 1, 2004||Markus Christoph||Method and apparatus for dynamic sound optimization|
|US20040158135 *||Feb 9, 2004||Aug 12, 2004||Nellcor Incorporated, A Delaware Corporation||Pulse oximeter sensor off detector|
|US20040181134 *||Mar 22, 2004||Sep 16, 2004||Nellcor Puritan Bennett Incorporated||Pulse oximeter with parallel saturation calculation modules|
|US20040193411 *||Jul 2, 2002||Sep 30, 2004||Hui Siew Kok||System and apparatus for speech communication and speech recognition|
|US20040252852 *||Mar 29, 2004||Dec 16, 2004||Taenzer Jon C.||Hearing system beamformer|
|US20050063558 *||Jun 21, 2002||Mar 24, 2005||Oticon A/S||Method for noise reduction and microphonearray for performing noise reduction|
|US20050085735 *||Oct 12, 2004||Apr 21, 2005||Nellcor Incorporated, A Delaware Corporation||Method and apparatus for estimating a physiological parameter|
|US20050111683 *||Sep 8, 2004||May 26, 2005||Brigham Young University, An Educational Institution Corporation Of Utah||Hearing compensation system incorporating signal processing techniques|
|US20050124871 *||Jan 19, 2005||Jun 9, 2005||Nellcor Puritan Bennett Incorporated||Pulse oximeter with parallel saturation calculation modules|
|US20050141731 *||Dec 16, 2004||Jun 30, 2005||Nokia Corporation||Method for efficient beamforming using a complementary noise separation filter|
|US20050143634 *||Mar 1, 2005||Jun 30, 2005||Nellcor Incorporated, A Delaware Corporation||Method and apparatus for estimating a physiological parameter|
|US20050147258 *||Dec 24, 2003||Jul 7, 2005||Ville Myllyla||Method for adjusting adaptation control of adaptive interference canceller|
|US20050207583 *||Mar 21, 2005||Sep 22, 2005||Markus Christoph||Audio enhancement system and method|
|US20060025994 *||Jul 20, 2005||Feb 2, 2006||Markus Christoph||Audio enhancement system and method|
|US20060072693 *||Dec 5, 2005||Apr 6, 2006||Bitwave Pte Ltd.||Signal processing apparatus and method|
|US20060183988 *||Apr 18, 2006||Aug 17, 2006||Baker Clark R Jr||Pulse oximeter with parallel saturation calculation modules|
|US20070046278 *||Aug 26, 2005||Mar 1, 2007||Step Communications Corporation, A Nevada Corporation||System and method for improving time domain processed sensor signals|
|US20070046540 *||Aug 26, 2005||Mar 1, 2007||Step Communications Corporation, A Nevada Corporation||Beam former using phase difference enhancement|
|US20070047742 *||Aug 26, 2005||Mar 1, 2007||Step Communications Corporation, A Nevada Corporation||Method and system for enhancing regional sensitivity noise discrimination|
|US20070047743 *||Aug 26, 2005||Mar 1, 2007||Step Communications Corporation, A Nevada Corporation||Method and apparatus for improving noise discrimination using enhanced phase difference value|
|US20070050161 *||Aug 26, 2005||Mar 1, 2007||Step Communications Corporation, A Neveda Corporation||Method & apparatus for accommodating device and/or signal mismatch in a sensor array|
|US20070050176 *||Aug 26, 2005||Mar 1, 2007||Step Communications Corporation, A Nevada Corporation||Method and apparatus for improving noise discrimination in multiple sensor pairs|
|US20070050441 *||Aug 26, 2005||Mar 1, 2007||Step Communications Corporation,A Nevada Corporati||Method and apparatus for improving noise discrimination using attenuation factor|
|US20070208242 *||Feb 1, 2007||Sep 6, 2007||Nellcor Puritan Bennett Inc.||Selection of ensemble averaging weights for a pulse oximeter based on signal quality metrics|
|US20080040078 *||Oct 9, 2007||Feb 14, 2008||Step Communications Corporation||Method and apparatus for improving noise discrimination in multiple sensor pairs|
|US20080137874 *||Nov 26, 2007||Jun 12, 2008||Markus Christoph||Audio enhancement system and method|
|US20080292107 *||Jan 23, 2008||Nov 27, 2008||Syfx Tekworks||Noise analysis and extraction systems and methods|
|US20080317261 *||Jun 19, 2008||Dec 25, 2008||Sanyo Electric Co., Ltd.||Wind Noise Reduction Device|
|US20090034747 *||Oct 6, 2008||Feb 5, 2009||Markus Christoph||Audio enhancement system and method|
|US20090234618 *||Dec 29, 2008||Sep 17, 2009||Step Labs, Inc.||Method & Apparatus For Accommodating Device And/Or Signal Mismatch In A Sensor Array|
|US20090304203 *||Sep 8, 2006||Dec 10, 2009||Simon Haykin||Method and device for binaural signal enhancement|
|US20110029288 *||Feb 3, 2011||Dolby Laboratories Licensing Corporation||Method And Apparatus For Improving Noise Discrimination In Multiple Sensor Pairs|
|US20110071375 *||Nov 23, 2010||Mar 24, 2011||Nellcor Incorporated, A Delaware Corporation||Method and apparatus for estimating physiological parameters using model-based adaptive filtering|
|US20110317858 *||Dec 29, 2011||Yat Yiu Cheung||Hearing aid apparatus|
|US20120057717 *||Sep 2, 2010||Mar 8, 2012||Sony Ericsson Mobile Communications Ab||Noise Suppression for Sending Voice with Binaural Microphones|
|US20120057719 *||Nov 8, 2011||Mar 8, 2012||Douglas Andrea||Adaptive filter in a sensor array system|
|US20140119568 *||Nov 1, 2012||May 1, 2014||Csr Technology Inc.||Adaptive Microphone Beamforming|
|US20140341397 *||May 15, 2013||Nov 20, 2014||Infineon Technologies Ag||Apparatus and Method for Controlling an Amplification Gain of an Amplifier, and a Digitizer Circuit and Microphone Assembly|
|USRE38476 *||Jun 27, 2002||Mar 30, 2004||Masimo Corporation||Signal processing apparatus|
|USRE38492||Mar 11, 2002||Apr 6, 2004||Masimo Corporation||Signal processing apparatus and method|
|DE4335843A1 *||Oct 20, 1993||Apr 27, 1995||Siemens Ag||Method for eliminating digital quasi-periodic noise signals|
|EP0545731A1 *||Dec 4, 1992||Jun 9, 1993||Sony Corporation||Noise reducing microphone apparatus|
|EP0558312A1 *||Feb 25, 1993||Sep 1, 1993||Central Institute For The Deaf||Adaptive noise reduction circuit for a sound reproduction system|
|EP0581262A1 *||Jul 28, 1993||Feb 2, 1994||Minnesota Mining And Manufacturing Company||Auditory prosthesis for adaptively filtering selected auditory component by user activation and method for doing same|
|EP0642290A2 *||Sep 2, 1994||Mar 8, 1995||Philips Patentverwaltung GmbH||Mobile communication apparatus with speech processing device|
|EP0652686A1 *||Oct 26, 1994||May 10, 1995||AT&T Corp.||Adaptive microphone array|
|EP0661904A2 *||Dec 4, 1992||Jul 5, 1995||Sony Corporation||Noise reducing microphone apparatus|
|EP0880870A1 *||Feb 14, 1997||Dec 2, 1998||Armand P. Neukermans||Improved biocompatible transducers|
|EP1224837A2 *||Oct 25, 2000||Jul 24, 2002||Andrea Electronics Corporation||Super directional beamforming design and implementation|
|WO1992015955A1 *||Mar 5, 1992||Sep 17, 1992||Vital Signals, Inc.||Signal processing apparatus and method|
|WO1995034983A1 *||Jun 13, 1995||Dec 21, 1995||Ab Volvo||Adaptive microphone arrangement and method for adapting to an incoming target-noise signal|
|WO1999021400A1 *||Oct 20, 1998||Apr 29, 1999||Technische Universiteit Delft||Hearing aid comprising an array of microphones|
|WO2000041436A1 *||Jan 5, 2000||Jul 13, 2000||Phonak Ag||Method for producing an electric signal or method for boosting acoustic signals from a preferred direction, transmitter and associated device|
|WO2000046928A1 *||Feb 4, 2000||Aug 10, 2000||Cassper Instrumentation Systems, Inc.||System and method for measuring rf radiated emissions in the presence of strong ambient signals|
|WO2007025033A2 *||Aug 25, 2006||Mar 1, 2007||Step Communications Corporation||Method and system for enhancing regional sensitivity noise discrimination|
|U.S. Classification||381/94.7, 381/71.11|
|International Classification||H04R25/00, H04R3/00|
|Cooperative Classification||H04R3/005, H04R25/505, H04R25/407|
|European Classification||H04R25/40F, H04R3/00B|
|Jun 12, 1989||AS||Assignment|
Owner name: MASSACHUSETTS INSTITUTE OF TECHNOLOGY, MASSACHUSET
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:PETERSON, PATRICK M.;REEL/FRAME:005150/0739
Effective date: 19890602
Owner name: MASSACHUSETTS INSTITUTE OF TECHNOLOGY, MASSACHUSET
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:GREENBERG, JULIE E.;REEL/FRAME:005150/0738
Effective date: 19890530
Owner name: MASSACHUSETTS INSTITUTE OF TECHNOLOGY, MASSACHUSET
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:ZUREK, PATRICK M.;REEL/FRAME:005150/0737
Effective date: 19890530
|Mar 24, 1994||FPAY||Fee payment|
Year of fee payment: 4
|Mar 24, 1994||SULP||Surcharge for late payment|
|Apr 7, 1998||REMI||Maintenance fee reminder mailed|
|Apr 29, 1998||SULP||Surcharge for late payment|
|Apr 29, 1998||FPAY||Fee payment|
Year of fee payment: 8
|Mar 26, 2002||REMI||Maintenance fee reminder mailed|
|Sep 11, 2002||LAPS||Lapse for failure to pay maintenance fees|
|Nov 5, 2002||FP||Expired due to failure to pay maintenance fee|
Effective date: 20020911